A pressure regulator of this type, which may be an integral part of the pump or may constitute a separate element, generally comprises throttling means movable against the action of elastic restoring means and interposed between a pipe for connection to a tank and a pipe for connection to the suction or intake port of the pump, the throttling means being displaceable by an element having one end received in a pipe or a chamber connectable to the delivery or discharge port of the pump, so that the delivery pressure acts on this element.
A pump provided with a regulator of the above type necessarily comprises a pressure limiter, inasmuch as one cannot be certain of the tightness of the throttling. If a leakage occurs in a position in which the connection between the tank and the suction port is supposed to be cut off, a pressure increase may occur which is to be controlled by the pressure limiter. Such a pressure limiter generally comprises a valve which opens against elastic means when the delivery pressure of the pump reaches a safety threshold, thereby connecting the delivery port of the pump with the tank.
Swiss Pat. No. 205 990 describes a pressure limiter of this type which is associated with a compressor and which, when the safety threshold is attained, isolates the suction port from the compressor and simultaneously places the delivery port thereof in communication with the tank, upstream of the pressure regulator. This results in that the suction port of the compressor is at an underpressure and that leakages may occur.